This is a collection of interesting/confusing parts of rust syntax.
Declaring parameters
error[E0384]: cannot assign twice to immutable variable `value`
--> src/second.rs:100:13
|
99 | list.peek_mut().map(|&mut value| {
| -----
| |
| first assignment to `value`
| help: make this binding mutable: `mut value`
100 | value = 42
| ^^^^^^^^^^ cannot assign twice to immutable variable ^~~~~
The compiler is complaining that value is immutable, but we pretty clearly
wrote &mut value; what gives?
It turns out that writing the argument of the closure that way doesn’t specify that value is a mutable reference. Instead, it creates a pattern that will be matched against the argument to the closure.
|&mut value| means “the argument is a mutable reference, but just copy
the value it points to into value, please.” If we just use |value|, the type of
value will be &mut i32.
Iterators
Iterator<Item = &'g Lime>> says:
“I can iterate over items that last as long as 'g”